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Performance of urinalysis tests and their ability in predicting results of urine cultures: a comparison between automated test strip analyser and flow cytometry in various subpopulations and types of samples

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Performance of urinalysis tests and their ability in predicting results of urine cultures: a comparison between automated test strip analyser and flow cytometry in various subpopulations and types of samples

Abstract

Aims Results of urinalysis are available earlier than urine culture results. If urinalysis can predict results of culture, early decision can be made on treatment and whether urine samples should be cultured. This study sought to compare the performance of urinalysis tests by automated test strip analyser (nitrite and leucocyte esterase) with flow cytometry (bacteria and white cell count) in different subpopulations and types of samples.

Methods Consecutive urine samples (n=2351) from a population with a median age of 45 years, 37.2% men, were tested. Sensitivity, specificity, positive predictive value and negative predictive value (NPV) of the tests were calculated using contingency tables. The gold standard was positive urine culture with cut-off >105 CFU/mL.

Results 14% of the cultures were positive (95.6% monomicrobial, 74.7% Enterobacteriaceae). Overall, nitrite test was the most specific (98.7%) but the least sensitive (43.2%). Bacteria count was the most sensitive (91.7%) and highly specific (87.5%). In infants <24 months, the sensitivity of bacteria count was reduced (86.1%), but specificity was high (95.9%). The specificity of nitrite was reduced in urine from the in-and-out procedure (81.9%). The sensitivity of bacteria count was reduced in bag specimens urine (83.3%) and in urine from indwelling catheter (84.7%). All tests showed a high NPV. The NPV of the combined flow cytometry tests was higher than those of automated test strip analyser (99.1% vs 97.4%).

Conclusions Overall, the performance of urinalysis is excellent. Flow cytometry tests performed better than automated test strip analyser in ruling out urine to be cultured.

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Footnotes

Handling editor Cheok Soon Lee

Contributors All authors contributed to the conception and design of the work. All authors performed the acquisition, analysis and interpretation of data. EY drafted the work. EY, BVH and JvH revised the work critically for important intellectual content. All authors gave final approval of the version to be published and agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

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